The use of cathode ray tube based instruments, such as oscilloscopes, to analyze internal combustion engine performance, has become prevalent in recent years. The increased use of these instruments is, in part, due to the increasing complexity of the electronic portion of internal combustion engines and, in part, due to the increasing technical capabilities of the persons analyzing such engines. The various uses of oscilloscopes to analyze internal combustion engines covers a broad spectrum, including measuring the electrical and mechanical timing of the engine, such as the coincidence of spark discharge to cylinder valve operation, and measuring the many electrical signals present in the controlling and monitoring systems of a modern internal combustion engine.
It is usually necessary to synchronize the trigger sweep of an oscilloscope to the test device being monitored in order for a meaningful oscilloscope display to be created. When the test device is an internal combustion engine, the synchronization between the oscilloscope and the engine under test may be obtained from different locations, depending upon the type of analysis to be performed. In some instances the synchronization signal is obtained from a reference cylinder spark plug wire. In other instances the synchronization signal is obtained from the primary winding of the ignition coil. The present invention involves processing the latter source of synchronization signals.
Unfortunately, primary winding derived synchronizing signals are noisy because the point opening and closing that causes spark discharge is not abrupt and precise. Furthermore, the inductive capacitive nature of the coil and condenser combination create complex signals. Contrariwise, in order to be useful, trigger pulses should have only one rising edge per cycle of ignition point opening and closing. Further, the rising edge should occur with minimal delay from the point in time when the ignition points break. While solid state, e.g., transistorized, ignition systems do not use points, such ignition systems also create complex signals at the primary winding of an ignition coil and thus, present the same problems. Because the spark discharge signals detected by a synchronizing test lead are complex and, thus, are unsuitable for triggering an oscilloscope in the form generated, it is necessary to process these signals. This invention is directed to such a processor. More specifically, this invention is directed to providing an ignition coil primary winding signal processing system that provides oscilloscope trigger pulses having only one rising edge per spark plug firing cycle. Further, the trigger pulses occur with minimal delay from the start of such a cycle, i.e., from the time ignition points break in the case of a breaker plate ignition system or the time a semiconductor switch opens in an electronic (e.g., transistorized) ignition system.
Ignition coil primary winding signals are normally used to measure the dwell angle or ignition duty cycle of an internal combustion engine. In the case of a breaker plate ignition system the dwell angle is the ratio of the measure of the time that the ignition points are closed to the measure of the time of one full open and close ignition point cycle. An equivalent ratio is produced by electronic ignition systems. The present invention is also directed to providing an ignition coil primary winding signal processing system that produces a voltage representative of the dwell angle of an internal combustion engine that includes either a breaker plate or an electronic ignition system.